Essentials of Ecology

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256 CHAPTER 11 Sustaining Aquatic Biodiversity


Trawler
fishing

Drift-net fishing

Purse-seine fishing

Long line fishing

lines with
hooks

Sonar

Fish farming
in cage Spotter airplane

Deep sea
aquaculture cage

Float Buoy

Fish caught
by gills

Figure 11-7 Major commercial fishing methods used to harvest various marine species. These methods have
become so effective that many fish species have become commercially extinct.

■ CASE STUDY


Industrial Fish Harvesting Methods


Industrial fishing fleets dominate the world’s marine
fishing industry. They use global satellite positioning
equipment, sonar, huge nets and long fishing lines,
spotter planes, and gigantic refrigerated factory ships
that can process and freeze their catches. These fleets
help meet the growing demand for seafood. But crit-
ics say that these highly efficient fleets are vacuuming
the seas, decreasing marine biodiversity, and degrading
important marine ecosystem services. Today 75% of
the world’s commercial fisheries are being fished at or
beyond their estimated sustainable yields, according to
the U.N. Food and Agricultural Organization.
Figure 11-7 shows the major methods used for the
commercial harvesting of various marine fishes and
shellfish. Until the mid-1980s, fishing fleets from de-

veloped countries dominated the ocean catch. Today,
most of these fleets come from developing countries,
especially in Asia.
Let us look at a few of these methods. Trawler fishing
is used to catch fishes and shellfish—especially shrimp,
cod, flounder, and scallops—that live on or near the
ocean floor. It involves dragging a funnel-shaped net
held open at the neck along the ocean bottom. It is
weighted down with chains or metal plates and scrapes
up almost everything that lies on the ocean floor and
often destroys bottom habitats—somewhat like clear-
cutting the ocean floor (Figure 11-3). Newer trawling
nets are large enough to swallow 12 jumbo jet planes
and even larger ones are on the way.
Another method, purse-seine fishing, is used to catch
surface-dwelling species such as tuna, mackerel, ancho-
vies, and herring, which tend to feed in schools near
the surface or in shallow areas. After a spotter plane lo-
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